Method and digital circuit for generating a waveform from stored digital values

a digital value and waveform technology, applied in the field of method and digital circuit for generating a waveform from stored digital values, can solve problems such as electromagnetic interference (emi), and achieve the effect of improving the performance characteristics of the pll

Inactive Publication Date: 2012-05-10
QUALCOMM INC
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0007]One particular advantage provided by at least one of the disclosed embodiments is that a waveform with a desired shape to be applied to a modulator coupled to a frequency divider may be implemented by storing appropriate digital values in a memory. The waveform of the desired shape may be selected for improved performance characteristics of the PLL.

Problems solved by technology

However, the output clock signal that is generated by such circuits may have a large power density at a single frequency resulting in electromagnetic interference (EMI).

Method used

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  • Method and digital circuit for generating a waveform from stored digital values
  • Method and digital circuit for generating a waveform from stored digital values
  • Method and digital circuit for generating a waveform from stored digital values

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Embodiment Construction

[0017]A clock synchronization circuit, such as a PLL, may be used to generate an output clock that is locked to a received reference clock. A feedback path of the clock synchronization circuit may include a frequency divider (e.g., a 1 / N divider) that is driven by a digital modulator. The digital modulator may be responsive to a seed value to drive the frequency divider. Electromagnetic interference (EMI) is reduced at the output clock by providing a seed value to the digital modulator that is a combination of a fixed value and a modulation value. A waveform generator at the clock synchronization circuit generates the modulation value from digital values stored in a memory, where the digital values may be selected for the generated waveform to take on a desired shape. The combined seed causes the average divisor value, N, of the frequency divider to vary over a small range. As a result, power density at the output clock can be spread over a small frequency band instead of being conc...

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Abstract

In a particular embodiment, a method includes adjusting an input to a divider on a feedback path of a phase locked loop circuit based on a stored digital value representing a portion of a time-based waveform that is applied to a modulator circuit. The stored digital value is retrieved based on an output of the feedback path.

Description

I. FIELD[0001]The present disclosure is generally related to a method and digital circuit for generating a waveform from stored digital values.II. DESCRIPTION OF RELATED ART[0002]Advances in technology have resulted in smaller and more powerful computing devices. For example, there currently exist a variety of portable personal computing devices, including wireless computing devices, such as portable wireless telephones, personal digital assistants (PDAs), and paging devices that are small, lightweight, and easily carried by users. More specifically, portable wireless telephones, such as cellular telephones and Internet Protocol (IP) telephones, can communicate voice and data packets over wireless networks. Many such wireless telephones incorporate additional devices to provide enhanced functionality for end users for example, a wireless telephone can also include a digital still camera, a digital video camera, a digital recorder, and an audio file player. Also, such wireless teleph...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): H03L7/06G06F19/00H03L7/00
CPCH03L7/1976
Inventor ZHU, ZHIKONG, XIAOHUADANG, NAM V.
Owner QUALCOMM INC
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